Browsing by Author "Kim, Y. S."

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    Ferroelectric enhancement of La-doped BaTiO3 thin films using SrTiO3 buffer layer
    (ELSEVIER, 2014) Ali, Ahmed I.; Park, Kibog; Ullah, Amir; Huh, Rock; Kim, Y. S.
    Pulsed laser deposition (PLD) was used to fabricate La0.01Ba0.99TiO3 (LBTO) thin films on MgO/TiO2/SiO2/Si substrates with and without SrTiO3 (STO) buffer layer. LBTO films deposited on STO layers exhibited enhanced ferroelectricity and decreased leakage current (9 x 10(-7) A/cm(2) at 50 kV/cm), conductivity, and Hall mobility, compared to those of LBTO films on MgO substrate. The remanent polarization (P-r) and coercive field (E-c) for LBTO thin films on STO buffered MgO substrate dramatically improved, 36.5 mu C/cm(2) and similar to 220 kV/cm, compared to those for LBTO thin films on MgO substrate, 3 mu C/cm(2) and similar to 60 kV/cm. The degradation of P-r and E-c after 10(5) switching test is less than 0.1% for LBTO thin films on STO buffered MgO substrate. This work demonstrates a route to a lead-free ferroelectric thin film for nonvolatile memories and electro-optic devices. (C) 2013 Elsevier B.V. All rights reserved.
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    Optical and dielectric results of Y0.225Sr0.775CoO3 +/-delta thin films studied by spectroscopic ellipsometry technique
    (ELSEVIER, 2013) Ali, A. I.; Son, J. Y.; Ammar, A. H.; Moez, A. Abdel; Kim, Y. S.
    Y0.225Sr0.775CoO3 +/-delta thin films have been deposited on SrTiO3 (111), SrTiO3 (100), LaAlO3 (100) and MgO (111) single crystals substrates at 500 degrees C by pulsed laser deposition (PLD) method. The optical measurements of these films were studied by ellipsometric method in the spectral range from 310 to 1240 nm. The dependence of the optical constants, the refractive index (n), the extinction coefficient (k), the dielectric loss (epsilon') and the dielectric tangent loss (epsilon '') of these films on the different single crystal substrates was also studied. The normal dispersion of refractive index of the films could be described using the Wemple-DiDomenico single oscillator method. The optical dispersion parameters E-o and E-d were determined according to the above oscillator method. Y0.225Sr0.775CoO3 +/-delta thin films on different substrates have two direct and indirect allowed transitions corresponding to the energy gap E-g(d) and E-g(ind). The variation in either E-g(d) or E-g(ind) with different substrates revealed that, orientation of the substrates affected the energy gap value. Other optical parameters such as the surface energy loss function and the volume energy loss function. were calculated optically. The effective mass of the film has also been calculated from both electrical and optical measurements. (C) 2013 The Authors Published. by Elsevier B.V. Open access under CC BY-NC-ND license.